Preparation of azo compounds having carboxyl and cyano groups

ABSTRACT

A process for the preparation of a diazocyano acid, which comprises reacting a keto-acid or its sodium salt with a cyanogen compound such as sodium cyanide or hydrogen cyanide and a hydrazine in water to form a concentrated aqueous solution of a hydrazo compound, adding acetone or acetone and water to the concentrated aqueous solution to form an acetone-water solution of the hydrazo compound, adding an oxidant such as chlorine gas to the solution to oxidize the hydrazo compound and form a diazocyano acid, forming at least two transparent liquid layers by adding acetone and/or water to the obtained reaction mixture during or after oxidation if necessary, and further adding sodium chloride to the reaction mixture if necessary, and separating and recovering the upper layer of the acetone-water solution containing the diazocyano acid from the mixture.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to a process for preparing a diazocyano acid such as 4,4'-azobis-(4-cyanovaleric acid) using a keto-acid such as levulinic acid or a sodium salt of keto-acid as the starting material.

2. Background Information

Diazocyano acids have been used as an initiator for polymerization such as homopolymerization of acrylamide or 1,3-butadiene or copolymerization of 1,3-butadiene with acrylonitrile (see, e.g., Japanese Examined patent publication (Kokoku) No. 43-28474 and Japanese Unexamined patent publication (Kokai) Nos. 56-133305 and 57-198720).

As means for the preparation of diazocyano acids, there is known a process comprising reacting a keto-acid or its sodium salt with a cyanogen compound such as sodium cyanide or hydrogen cyanide and a hydrazine such as hydrazine hydrate or hydrazine sulfate in water to form a hydrazo compound, adding chlorine gas to the obtained solution to oxidize the hydrazo compound and form a diazocyano acid and filtering off the solid diazocyano acid from the obtained reaction mixture (see, also, Japanese Examined patent publication (Kokoku) No. 43-28474 and Japanese Unexamined patent publication (Kokai) No. 56-133305).

However, this known process has the following problems:

(a) Since sodium chloride is formed as a by-product in an amount of at least 2 moles per mole of a diazocyano acid when the diazocyano acid is synthesized, a large amount of sodium chloride is contained in the diazocyano acid product. A diazocyano acid containing a large amount of sodium chloride is not preferred as the initiator for homopolymerization of 1,3-butadiene or copolymerization of 1,3-butadiene with acrylonitrile.

(b) If a refining step is arranged for removing sodium chloride contained in the diazocyano acid, the yield of the diazocyano acid is drastically reduced.

SUMMARY OF THE INVENTION

The inventors conducted extensive research with a view to developing a novel process for the preparation of diazocyano acids in which the above-mentioned problems are overcome, and as the result, we have completed the present invention.

More specifically, in accordance with the present invention, there is provided a process for the preparation of a diazocyano acid, which comprises reacting a keto-acid or its sodium salt with a cyanogen compound such as sodium cyanide or hydrogen cyanide and a hydrazine in water to form a concentrated aqueous solution of a hydrazo compound, adding acetone or acetone and water to the concentrated aqueous solution to form an acetone-water solution of the hydrazo compound, adding an oxidant such as chlorine gas to the solution to oxidize the hydrazo compound and form a diazocyano acid, forming at least two transparent liquid layers by adding acetone and/or water to the obtained reaction mixture during or after oxidation if necessary, and further adding sodium chloride to the reaction mixture if necessary, and separating and recovering the uppermost layer of the acetone-water solution containing the diazocyano acid and if necessary, separating the diazocyano acid from the solution.

According to the present invention, diazocyano acids can be prepared in a high yield.

Furthermore, according to the present invention, the mixture of acetone and water is formed into two liquid layers containing the diazocyano acid and sodium chloride, respectively, by adjusting the ratio of acetone to water in the resulting reaction mixture within a specific range, preferably from 80/20 to 33/67, especially from 80/20 to 60/35, and thus, the upper layer of the acetone-water solution containing the diazocyano acid can be separated very easily. Therefore, the process of the present invention is industrially advantageous.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the process of the present invention, it is preferred that a keto-acid or its sodium salt (per 1 mole) be reacted with a cyanogen compound (0.95 to 1.5 mole, more preferably 1 mole) and a hydrazine (0.45 to 0.6 mole, more preferably 0.5 mole) in the presence or absence of a mineral acid such as hydrochloric acid or an alkali such as sodium hydroxide in a small amount of water, and a concentrated aqueous solution of a hydrazo compound may be obtained according to any of the following processes.

The aqueous solution of the hydrazo compound may be in a slurry state or in a transparent liquid state.

(a) When the hydrazo compound is formed by reacting a keto-acid or its sodium salt with a mixture of the cyanogen compound such as sodium cyanide or hydrogen cyanide and the hydrazine. This reaction is carried out, preferably at a temperature of not higher than 50° C., especially 15° to 40° C., in the presence of water in an amount of 10 to 200 parts, especially 15 to 100 parts by weight per 100 parts by weight of the keto-acid or its sodium salt.

(b) When the hydrazo compound is formed by contacting a keto-acid or its sodium salt with the cyanogen compound such as sodium cyanide or hydrogen cyanide and contacting the reaction product with the hydrazine to form cyanohydrin, the reaction is carried out, preferably at a temperature of not higher than 50° C., especially not higher than 20° C., in the presence of water in an amount of 80 to 200 parts by weight per 100 parts by weight of the keto-acid or its sodium salt.

(c) A keto-acid or its sodium salt is reacted with the hydrazine in water in an amount of 50 to 500 parts, especially 50 to 200 parts by weight per 100 parts by weight of the keto-acid or its sodium salt to form a ketazine, and the ketazine is reacted with the cyanogen compound such as hydrogen cyanide or sodium cyanide to form a concentrated aqueous solution of the hydrazo compound. Preferably, the reaction temperature is not higher than 100° C., especially 5° to 35° C.

It is preferred that, in the formation of the hydrazo compound by each process (a) to (c) as mentioned above, the pH value of the reaction system is adjusted to 5 to 9, especially 5.5 to 7.3 after the addition of the respective reactants. The pH value may be adjusted in a usual manner, for example, by addition of an aqueous NaOH or HCl.

Where a concentrated aqueous solution of the hydrazo compound is not employed, the yield of the diazocyzano acid may be low.

Among the processes (a) to (c), the process (c) is particularly preferred.

As a preferred example of the keto-acid, there can be mentioned levulinic acid.

As a preferred example of the diazocyano acid, there can be mentioned 4,4'-azobis-(4-cyanovaleric acid).

As examples of the hydrazine, there can be mentioned hydrazine hydrate.

According to the process of the present invention, there may be obtained, for example, a concentrated aqueous solution of the reaction product, that is, a hydrazo compound of the following formula, at the above-mentioned step: ##STR1## wherein R stands for alkyl of 1 to 6 carbon atoms, M stands for Na or H, and n is an integer of 1 to 6.

In the present invention, acetone or an acetone-water mixed solvent is added to the above-mentioned concentrated aqueous solution to form an acetone-water solution of the hydrazo compound in which the acetone/water volume ratio is preferably from 80/20 to 33/67, more preferably from 80/20 to 65/35.

Where an unreacted cyanogen compound (NaCN, HCN) or hydrazine may be retained in the above-mentioned concentrated aqueous solution of the hydrazo compounds, it is preferred that chlorine gas is added to the solution, after the addition of water as required, to react it with the unreacted compound, and thereafter, acetone or acetone and water are added to form an acetone-water solution containing the hydrazo compound and then chlorine gas is added to oxidize the hydrazo compound.

In the process of the present invention, an oxidant such as chlorine gas is added to the above solution preferably in an amount of at least 0.5 mole, more preferably 0.5 to 1 mole, especially 0.5 to 0.75 mole, per mole of the keto-acid or its sodium salt to oxidize the hydrazo compound and form the diazocyano acid. It is preferred that this oxidation reaction be carried out at a temperature lower than 30° C., especially lower than 15° C.

Addition of the oxidant can be performed according to known procedures at the above-mentioned oxidizing step.

In the process for the present invention, the acetone/water volume ratio in the so-obtained reaction mixture containing the diazocyano acid is preferably adjusted to from 80/20 to 33/67, especially from 80/20 to 65/35, if necessary by adding acetone and or water to the reaction mixture, and sodium chloride is further added if necessary, whereby the reaction mixture is formed into two liquid layers, at least the upper layer of which is transparent. The upper layer of the acetone-water solution containing the diazocyano acid is separated and recovered preferably at a temperature of 0° to 50° C., especially 15° to 50° C.

In the process of the present invention, when the diazocyano acid is formed by the above-mentioned oxidation reaction, sodium chloride is formed as a by-product in an amount of at least 2 moles per mole of the diazocyano acid. In the process of the present invention, by adjusting the ratio of acetone to water in the reaction mixture, sodium chloride formed as the by-product is dissolved or partially precipitated in the lower layer (containing a small amount of acetone) and only a very small amount of sodium chloride is dissolved in the upper layer of the acetone-water solution having the diazocyano acid dissolved therein. Furthermore, if sodium chloride is added afresh to the mixture having the two separated layers, the proportion of the lower layer is increased and the amount of water in the diazocyano acid-containing acetone-water solution of the upper layer is decreased. Accordingly, the amount of sodium chloride contained in the acetone-water solution of the diazocyano acid becomes smaller than before the addition of sodium chloride. It is preferred that to sodium chloride to be added afresh until the volumes of the two layers do not change any more or a small amount of NaCl is retained undissolved in the lower layer.

If the ratio of acetone to water in the mixtue is outside the above-mentioned range when the diazocyano acid-containing acetone-water solution is separated and recovered, the mixture may not be separated into two layers or the separation may be difficult. If the ratio of acetone to water is within the above-mentioned range, especially, from 75/25 to 50/50, sodium chloride need not be added afresh or the amount of sodium chloride to be added afresh can be reduced, and the operation of recovering the upper layer from the two liquid layers is facilitated and can be accomplished by an ordinary separating method.

In the process of the present invention, in the case where hydrochloric acid is contained in the reaction mixture, it is preferred that a alkaline compound such as sodium hydroxide, sodium carbonate or sodium hydrogen-carbonate be added to neutralize hydrochloric acid and adjust the pH value of the solution to 3 to 5, especially 3 to 4.5.

In the process of the present invention, the diazocyano acid may be recovered by evaporating and removing acetone and water from the diazocyano acid-containing acetone-water solution and adding a small amount of water to the residual solid to effect water washing, or preferably, there may be adopted a method in which acetone is evaporated, water is added to the residue and the diazocyano acid is recovered by filtration. It is preferred that water be added to the residue left after evaporation of acetone in an amount of 100 to 1000 parts by weight, especially 100 to 500 parts by weight, per 100 parts by weight of the diazocyano acid, and the solid diazocyano acid be separated and recovered at a temperature lower than 30° C., especially lower than 10° C., particularly after mixing the liquid homogeneously. If necessary, the recovered diazocyano acid may be dried under reduced pressure to remove a small amount of water contained in the diazocyano acid crystal.

According to the process as mentioned above, a diazocyano acid having an Na content lower than 3000 ppm, especially lower than 600 ppm can be prepared in a high yield, and if water washing is repeated several times, the Na content can be greatly reduced.

The diazocyano acid obtained by the above-mentioned process of the present invention may be purified to further reduce the Na content by dissolving the resulting diazocyano acid in a mixed solution of acetone and water at a volume ratio of from 75/25 to 95/5, preferably 75/25 to 90/10, evaporating acetone from the solution and washing the residue with water. By this purification procedure, the Na content of the diazocyano acid can be reduced to a level of lower than 5 ppm. It is preferred that the diazocyano acid having an Na content lower than 8000 ppm, especially lower than 3000 ppm, be dissolved in the above-mentioned acetone-water solution.

It is preferred that the amount of the diazocyano acid is 1 to 60 g, especially 5 to 30 g, per 100 ml of the acetone-water solution. It is also preferred that the diazocyano acid be dissolved in the acetone-water solution at a temperature lower than 50° C., especially lower than 40° C. Acetone is removed by evaporation from the acetone-water solution containing the diazocyano acid (it is not necessary to completely remove acetone at this step), and the diazocyano acid precipitated in the remaining aqueous solution is separated, recovered and washed with water. There is preferably adopted a process in which water is added to the precipitated diazocyano acid in the aqueous solution to effect water washing and the diazocyano acid is recovered by filtration.

In the above-mentioned process, it is preferred that evaporation of acetone from the acetone-water solution containing the diazocyano acid be carried out at a temperature lower than 50° C., especially lower than 40° C. It also is preferred that acetone be evaporated until the acetone/water volume ratio is from 25/75 to 0/100, especially from 10/90 to 0/100 before filtration.

In the process, preferably, water is added to the residue left after the above-mentioned step of evaporation of acetone in an amount of 100 to 1500 parts by weight, especially 100 to 1000 parts by weight, per 100 parts by weight of the diazocyano acid, preferably followed by mixing, and the solid diazocyano acid is separated and recovered at a temperature lower than 10° C., preferably lower than 3° C. Separation and recovery of the diazocyano acid can be accomplished by known means.

It is preferred that the diazocyano acid separated and recovered at the above-mentioned step be washed with water in an amount of 50 to 400 parts by weight, especially 100 to 250 parts by weight, per 100 parts by weight of the diazocyano acid at a temperature lower than 10° C., especially lower than 3° C. If necessary, a small amount of water contained in the diazocyano acid may be removed by drying reduced pressure.

According to the above-mentioned process, a diazocyano acid having an Na content lower than 5 ppm can be obtained at a recovery ratio higher than 90%, and if the above-mentioned procedures are repeated on the so-obtained diazocyano acid having the reduced Na content, further purified diazocyano acid can be obtained.

The diazocyano acid prepared according to the process of the present invention can be used as the initiator for homopolymerization of 1,3-butadiene or copolymerization of 1,3-butadiene with acrylonitrile. Further, the diazocyano acid-containing acetone-water solution formed as the upper layer according to the process of the present invention can be used as the initiator solution without isolating the diazocyano acid.

It is preferred that the polymerization temperature be 70° to 130° C. and the polymerization time be 1 to 40 hours. It is preferred that the amount of the diazocyano acid be 5 to 20 parts by weight per 100 parts by weight of the monomer component (1,3-butadiene or the sum of 1,3-butadiene and acrylonitrile). The method for the addition of the diazocyano acid or the acetone-water solution containing the diazocyano acid is not particularly critical. The solution may be added intermittently or continuously. It is preferred that a carboxyl-terminated liquid polymer having an acrylonitrile content of up to 45% by weight, especially 15 to 35% by weight, a number average molecular weight of 1000 to 5000 and a functional group number of 1.8 to 2.5 per mole be formed by appropriately adjusting the polymerization conditions.

The so-separated liquid polymer may be mixed with an antioxidant according to a known method.

Unreacted 1,3-butadiene is removed from the polymerization reaction mixture if necessary, and water is added to the polymerization reaction mixture to wash the liquid polymer and the liquid polymer is separated and recovered. It is preferred that the liquid polymer be dried in an evaporator until the weight is not changed any more. Thus, the intended carboxyl-terminated polymer is obtained.

It is preferred that the amount of water added at this step be 100 to 400 parts by weight per 100 parts by weight of the carboxyl-terminated liquid polymer.

In the case where unreacted 1,3-butadiene is not removed from the polymerization reaction mixture, it is preferred that water be added so that the amount of acetone is 50 to 300 parts by weight, the amount of 1,3-butadiene is 10 to 100 parts by weight and the amount of water is 100 to 400 parts by weight per 100 parts by weight of the carboxyl-terminated liquid polymer. After the addition of water, mixing is preferably carried out to disperse the polymer, and when the mixture is allowed to stand still, preferably for 2 minutes to 10 hours, the mixture is separated into the phase of the liquid polymer-acetone solution and the phase of the acetone-water solution. The liquid polymer is separated and recovered from this mixture. If necessary, a small amount of water contained in the liquid polymer-acetone solution may be removed by centrifugal separation.

In the process of the present invention, by separating the liquid polymer from the acetone-water solution, water-soluble compounds formed as by-products at the step of preparing the diazocyano acid are removed in the state dissolved in the acetone-water solution. Furthermore, substantially all of a small amount of sodium chloride contained in the acetone-water solution of the diazocyano acid used as the polymerization initiator is removed from the liquid polymer.

The so-separated liquid polymer is dried in an evaporator until the weight is not changed any more.

As the evaporator, there may be used centrifugal film evaporators such as a lateral centrifugal film evaporator, a vertical centrifugal film evaporator and a VL-type centrifugal film evaporator.

The carboxyl-terminated liquid polymer prepared according to the process of the present invention can be used for the production of electro-deposition paints and powder paints and IC packaging materials.

The present invention will now be described in detail with reference to the following examples and comparative examples. In the examples, the pH of the reaction mixture was adjusted to 4 after the addition of all the three reaction components.

EXAMPLE 1

A 1-liter 4-neck flask equipped with a stirrer, a gas-introducing pipe, a gas vent and a dropping pipe was charged with 25.25 g (0.53 mole) of NaCN, 15 ml of H₂ O and 12.52 g (0.25 mole) of NH₂ NH₂. H₂ O, and the mixture was stirred at 25° C. A part of NaCN was left granular even after stirring. Then, a liquid formed by adding 8 g of concentrated HCl to 58 g (0.5 mole) of levulinic acid was dropped to the mixture while maintaining the reaction temperature at 25° to 28° C. A faintly yellow, slightly viscous slurry was formed and the insoluble granules of NaCN disappeared during the dropwise addition. After completion of the dropwise addition, the temperature was elevated to 35° C. and reaction was carried out for 2 hours at this temperature. The mixture was kept in the slurry state. The mixture was cooled to 5° C., and 540 ml of acetone and 36 ml of H₂ O cooled to 5° C. were added to the mixture. Then, 21.3 g (0.3 mole) of Cl₂ gas was blown into the mixture with violent stirring while cooling the mixture so that the reaction temperature did not exceed 10° C. After the reaction, the temperature was returned to 20° C. and 200 ml of water was added, and the mixture was stirred and allowed to stand still to separate the mixture into two liquid layers. The acetone/water volume ratio in the mixture at this point was 67.7/32.3. The formed liquid was transferred into a separating funnel and 10 g of NaCl was added, and the mixture was shaken and allowed to stand still. The lower layer having NaCl granules precipitated therein was removed, and the faintly yellow transparent upper layer was maintained at 20° C. and acetone was removed by distillation using an aspirator to precipitate a large amount of 4,4'-azobis-(4-cyanovaleric acid) (hereinafter referred to as ACVA). The temperature was lowered to 5° C. and ACVA was recovered by suction filtration. The recovered ACVA was dried under reduced pressure at 20° C. until the weight was not changed, whereby 63.50 g of pure-white ACVA was obtained. The yield was 90.6% based on levulinic acid. One peak was observed by the liquid chromatography. The results of the elementary analysis of ACVA (C₁₂ H₁₆ N₄ O₄) were as follows:

Calculated Values: C=51.43%, H=5.75%, N=19.99%.

Found Values: C=51.29%, H=5.58%, N=20.04%.

The Na content in ACVA was 430 ppm as determined by the atomic absorption spectroscopy.

EXAMPLE 2

A concentrated aqueous solution of a hydrazo compound was prepared in the same manner as described in Example 1, and this aqueous solution in the form of a slurry was cooled to 5° C. and 540 ml of acetone and 240 ml of H₂ O cooled to 5° C. were added. Then, 21.3 g (0.3 mole) of Cl₂ gas was blown into the mixture while cooling the mixture so that the reaction temperature did not exceed 10° C. If stirring was stopped after the reaction, the mixture was separated into two liquid layers. The formed liquid was transferred into a separating funnel, and 10 g of NaCl was added to the mixture and the mixture was shaken and allowed to stand still. The lower layer having NaCl granules precipitated therein was removed and the faintly yellow transparent upper layer was recovered. The post treatment and drying were carried out in the same manner as described in Example 1 to obtain 62.81 g of pure-white ACVA. The yield was 89.6% based on levulinic acid. One peak was observed by the liquid chromatography. The results of the elementary analysis of ACVA (C₁₂ H₁₆ N₄ O₄) were as follows:

Calculated Values: C=51.43%, H=5.75%, N=19.99%.

Found Values: C=51.44%, H=5.76%, N=19.97%.

The Na content in ACVA was 493 ppm as determined by the atomic absorption spectroscopy.

EXAMPLE 3

A 1-liter 4-neck flask equipped with a stirrer, a gas-introducing pipe, a gas vent and a dropping pipe was charged with 58.0 g (0.5 mole) of levulinic acid, 3.5 g of concentrated HCl and 5 ml of H₂ O. While the reaction temperature was maintained at 5° C., an aqueous solution of 25.25 g (0.53 mole) of NaCN in 50 ml of H₂ O was dropped to the mixture. Solidification was promptly caused at the final stage of the dropwise addition. Then, 7 g of concentrated HCl and 12.52 g (0.25 mole) of NH₂ NH₂.H₂ O were added to the reaction mixture and the temperature was elevated to 35° C. When the temperature exceeded the level of 20° C., stirring became possible, and at 33° C. the slurry was converted to a faintly yellow transparent liquid. Reaction was carried out at 35° C. for 3 hours, and the reaction mixture was cooled to 5° C. and 540 ml of acetone was added thereto. Then, 21.3 g (0.3 mole) of Cl₂ gas was blown into the liquid while maintaining the liquid temperature below 10° C. After the reaction, the temperature was returned to 20° C., and 200 ml of H₂ O was added to the reaction mixture and the mixture was stirred and allowed to stand still, whereby the mixture was separated into two liquid layers. The subsequent operations were conducted in the same manner as described in Example 1 to obtain 56.9 g of pure-white ACVA. One peak was observed by the liquid chromatography. The results of the elementary analysis of ACVA (C₁₂ H₁₆ N₄ O₄) were as follows:

Calculated Values: C=51.34%, H=5.75%, N=19.99%.

Found Values: C=51.40%, H=5.74%, N=19.98%.

The Na content in ACVA was 510 ppm as determined by the atomic absorption spectroscopy.

EXAMPLE 4

A 2-liter 4-neck flask equipped with a stirrer, a gas-introducing pipe and a dropping pipe was charged with 58.0 g (0.5 mole) of levulinic acid and 50 ml of H₂ O, and the charge was cooled to 5° C. Then, 12.52 g (0.25 mole) of hydrazine hydrate was dropped to the charge so that the liquid temperature did not exceed 10° C. At this point, the mixture was a colorless viscous slurry. For about 15 minutes from the point of completion of the dropwise addition, stirring was conducted below 10° C., and an aqueous solution of 25.25 g (0.53 mole) of NaCN in 50 ml of H₂ O was added to the mixture so that the liquid temperature did not exceed 10° C. Midway in the addition of the aqueous solution, the mixture was converted to a faintly yellow transparent liquid from the slurry. Then, 2.5 g of concentrated HCl was added to the mixture to adjust the pH value to 7.0. The temperature was elevated to 20° C. and the liquid was stirred for 15 hours at this temperature. Then, the reaction mixture was cooled to 5° C. and 700 ml of acetone was added to the mixture, and 21.3 g (0.3 mole) of Cl₂ gas was blown into the mixture so that the temperature did not exceed 10° C. After the reaction, the temperature was returned to 20° C., and 230 ml of water was added to the reaction mixture so that the acetone/water volume ratio was 67/33. When the reaction mixture was stirred and allowed to stand still, the mixture was separated into two liquid layers. The subsequent operations were conducted in the same manner as described in Example 1 to obtain 58.9 g of pure-white ACVA. The yield was 84% based on levulinic acid. The results of the elementary analysis were in agreement with the calculated values of ACVA (C₁₂ H₁₆ N₄ O₄). The Na content in ACVA was 498 ppm.

EXAMPLE 5

A flat bottom flask having a capacity of 1 liter was charged with 50 g of dried ACVA (having an Na content of 498 ppm and obtained as in Example 4), and 300 ml of an acetone-water mixed solvent (A/W=75/25) was added and ACVA was dissolved therein at a temperature lower than 40° C. Then, acetone was removed by distillation under reduced pressure at a temperature lower than 40° C., whereby ACVA was gradually precipitated in water. After acetone had been completely removed, 300 ml of distilled water was added to the solution having ACVA precipitated therein. The mixture was stirred under cooling to 1° to 3° C. for 30 minutes and suction filtration was carried out by using G4 glass filter, and the recovered solid was washed with 100 ml of distilled water (1° to 3° C.) two times and dried under reduced pressure in the presence of P₂ O₅ to recover 47.1 g (94%) of ACVA having an Na content of 1.3 ppm as determined by the atomic absorption spectroscopy.

Then, a flat bottom flask having a capacity of 500 ml was charged with 30.0 g of the sample obtained above, and 250 ml of an acetone-water mixed solvent (A/W=75/25) was added and the sample was dissolved therein at a temperature lower than 40° C. When acetone was removed by distillation under reduced pressure, ACVA was gradually precipitated in water. After acetone had been completely removed, 100 ml of distilled water was added to the solution having ACVA precipitated therein and the mixture was stirred under cooling to 1° to 3° C. for 30 minutes. Suction filtration was performed by G4 glass filter and the solid was washed with 100 ml of distilled water (1° to 3° C.) two times and dried under reduced pressure in the presence of P₂ O₅ to recover 27.6 g (92%) of ACVA having an Na content of 0.3 ppm as determined by the atomic absorption spectroscopy.

COMPARATIVE EXAMPLE 1

A reaction vessel equipped with a stirrer, a gas-introducing pipe, a gas vent and a dropping pipe was charged with 0.963 kg (8.3 mole) of levulinic acid and 1.0 l of water, and the mixture was cooled to 5° C. After addition of 0.058 kg of concentrated hydrochloric acid and 0.3 l of water, a solution of 0.420 kg (8.5 mole) of NaCN in 1.6 l of water was added dropwise to the mixture while cooling the mixture so that the reaction temperature did not exceed 10° C., and thereafter, the mixture was left to react at a temperature not higher than 10° C. for 15 minutes. No product was precipitated, unlike in Example 1. To the mixture 0.208 kg (4.15 mole) of NH₂ NH₂.H₂ O was added dropwise, and the mixture was left to react at 35° C. for 3 hours. The mixture was then cooled to 5° C., added with 3.3 l of acetone and then with 0.31 kg (4.4 mole) of Cl₂ gas, and left to react while keeping the temperature below 10° C. Acetone was removed by distillation under reduced pressure from the reaction mixture in which ACVA was partially precipitated to precipitate a large amount of ACVA. Crude ACVA was obtained by suction filtration over the period of 3 hours. The crude ACVA was washed with 0.7 l of water, filtered, and dried under reduced pressure to obtain 0.69 kg of ACVA. The NaCl content in ACVA was 2000 ppm.

EXAMPLE 6

A 20-liter 4-neck flask equipped with a stirrer, a gas-introducing pipe, a gas vent and a dropping pipe was charged with 284.8 g (5.811 mole) of NaCN, 165 ml of H₂ O and 137.3 g (2.741 mole) of NH₂ NH₂ H₂ O, and the mixture was stirred at 25° C. A major of NaCN was left granular even after stirring. Then, a liquid formed by adding 54.8 g of concentratred HCl to 636.6 g (5.483 mole) of levulinic acid was added dropwise to the mixture while maintaining the reaction temperature at 20 to 22° C. A faintly yellow, slightly viscous slurry was formed and the insoluble granules of NaCN disappeared during the dropwise addition. To the mixture 54.8 g of concentrated HCl was added, the temperature was elevated to 35° C. and reaction was carried out for 1 hour at this temperature. The mixture was then cooled to 5° C. with ice water and left to stand for 2 hours. The mixture was kept in a white slurry state. The mixture was cooled to 3° C., 494 ml of water was added while again starting stirring, and 6372 ml of acetone of 4° C. was added to the mixture. Then, 233 g (3.29 mole) of Cl₂ gas was blown into the mixture while cooling the mixture so that the reaction temperature did not exceed 10° C. The mixture was added with 2.3 l of distilled water, stirred at 20° C., and the stirring was stopped. Thus, the mixture was clearly separated into two layers. The upper acetone solution layer was recovered by a separating funnel in an amount of 7.2 l. The acetone solution contained 697 g of ACVA. The Na content was 500 ppm.

This liquid was used as an initiator solution for poly-merization. A 35 l autoclave equipped with a magnetic stirrer, a thermometer, a charge-injection pipe, a coiled condenser and a vent was charged with 5275 g of 1,3-butadiene, 1136 g of acrylonitrile and 755 g of acetone, and the mixture was heated to 85° C. At this temperature, 630 ml of the initiator solution which contained 60 g of ACVA was injected into the autoclave. Additional portions of ACVA and acrylonitrile were added every 30 minutes according to the following addition program.

    ______________________________________                                         Hrs. from                Hrs. from                                             starting                                                                               Acrylo-          starting Acrylo-                                      polymeri-                                                                              nitrile  ACVA    polymeri-                                                                               nitrile                                                                               ACVA                                  zation  (g)      (g)     zation   (g)    (g)                                   ______________________________________                                         0.5     34.5     38.5    9.5      19.2   14.5                                  1.0     33.9     35.8    10.0     18.6   13.9                                  1.5     32.4     33.7    10.5     17.7   13.3                                  2.0     31.2     31.6    11.6     17.4   12.9                                  2.5     30.3     29.8    11.5     16.8   12.9                                  3.0     29.1     28.0    12.0     16.2   12.6                                  3.5     28.2     26.2    12.5     15.6   12.3                                  4.0     27.3     24.7    13.0     15.3   12.0                                  4.5     26.4     23.5    13.5     14.7   11.7                                  5.0     25.5     22.0    14.0     14.1   11.4                                  5.5     24.6     21.1    14.5     13.8   11.1                                  6.0     24.0     19.9    15.0     13.2   10.8                                  6.5     23.1     19.0    15.5     12.9   10.5                                  7.0     22.2     18.1    16.0     12.6   10.5                                  7.5     21.6     17.2    16.5     12.0   10.2                                  8.0     21.0     16.3    17.0     11.7   9.9                                   8.5     20.4     15.7    17.5     11.1   9.9                                   9.0     19.5     15.1                                                          ______________________________________                                    

The polymerization time was 18 hours, and the polymerization temperature was maintained at 85° C. ±0.2° C. except for the temperature drops within 2° C. for about 2 minutes at the time of the addition of the acrylonitrile and ACVA.

After the polymerization for 18 hours, ice water was introduced into the coiled condenser and the autoclave was dipped into ice water to rapidly cool the reaction mixture and stop the polymerization. 20,000 g of water was added to 14200 g of the polymerization liquid, and the mixture was stirred and then left to stand. Thus, the mixture was rapidly separated into two layers. The lower water-acetone layer was removed, and the upper polymer layer was added with 5000 g of acetone to dissolve the polymer. Then 8500 g of water was added, and the mixture was stirred and then left to stand for 3 hours. After the separation of the mixture into two layers, the lower layer was removed and the upper polymer layer was dried in a centrifugal film evaporator until the weight was not changed any more, whereby 6260 g of a carboxyl-terminated liquid polymer was obtained. The monomer conversion was 81.5%.

This liquid copolymer had an acrylonitrile content of 24.9 mole %, an acid value of 1830 g/eq, and an Na content of 31.0 ppm as measured by atomic-absorption spectroscopy. The ratio of the molecular-weight distribution indices Mw/Mn was 1.96.

EXAMPLE 7

The upper acetone solution layer as in Example 6 was obtained in an amount of 108 l. Acetone was distilled off from the acetone solution under reduced pressure, 3 l of water was added to form a slurry, and the slurry was stirred at 5° C. for 1 hour, filtered, and washed with 7 l of water of 5° C. Thus, 1572 g of wet ACVA was obtained. The wet ACVA was dissolved in a mixture of 8.5 l of acetone and 0.55 l of water. The resultant acetone-water solution of ACVA contained 945 g of ACVA and had an Na content of 56 ppm.

Using the acetone-water solution of ACVA, the polymerization procedure as in Example 6 was repeated, and the resultant polymer was washed with water and dried.

Thus, 6350 g of a carboxyl-terminated butadieneacrylonitrile copolymer was obtained. This copolymer had an acrylonitrile content of 25.1%, an acid value of 1910 g/eq, and an Na content of 2.3 ppm as measured by atomic-absorption spectroscopy. 

We claim:
 1. A process for the preparation of a diazocyano acid, which comprises reacting a keto-acid with sodium cyanide and a hydrazine of reacting a sodium salt of a keto-acid with hydrogen cyanide and a hydrazine, in the presence of water in an amount of not more than 200 parts by weight of water per 100 parts by weight of the keto-acid or its sodium salt to form a concentrated aqueous solution of a hydrazo compound, adding acetone or acetone in water to the concentrated aqueous solution to form an acetone-water solution of the hydrazo compound so that a volume ratio of 80/20 to 65/35 of acetone to water in a reaction mixture containing a dyazocyano acid and resulting from the next oxidation step is attained, adding an oxidant to the solution to oxidize the hydrazo compound and form the diazocyano acid, forming at least two transparent liquid layers by adding acetone or acetone and water to the obtained reaction mixture during or after oxidation if necessary, and further adding sodium chloride to the reaction mixture if necessary, and separating the upper layer of the acetone-water solution containing the diazocyano acid and recovering the diazocyano acid from the separated acetone-water solution.
 2. A process according to claim 1, wherein 1 mole of the keto-acid or its sodium salt is reacted with 0.95 to 1.5 moles of the cyanogen compound and 0.45 to 0.6 moles of the hydrazine.
 3. A process according to claim 1, wherein the concentrated aqueous solution of the hydrazo compound is formed by reacting the keto-acid or its sodium salt with a mixture of the cyanogen compound and the hydrazine in water.
 4. A process according to claim 3, wherein the amount of water is 10 to 200 parts by weight per 100 parts by weight of the keto-acid of its sodium salt.
 5. A process according to claim 1 wherein the concentrated aqueous solution of the hydrazo compound is formed by reacting the keto-acid or its sodium salt with the cyanogen compound in water to form cyanohydrin and reacting the cyanohydrin with the hydrazine.
 6. A process according to claim 5, wherein the reaction of the keto-acid or its sodium salt with the cyanogen compound is carried out at a temperature lower than 20° C.
 7. A process according to claim 5, wherein the amount of water is 80 to 200 parts by weight per 100 parts by weight of the keto-acid or its sodium salt.
 8. A process according to claim 1, wherein the concentrated aqueous solution of the hydrazo compound is formed by reacting the keto-acid or its sodium salt with the hydrazine in water to form a ketazine and reacting the ketazine with the cyanogen compound.
 9. A process according to claim 8, wherein the amount of water is 50 to 200 parts by weight per 100 parts by weight of the keto-acid or its sodium salt.
 10. A process according to claim 1, wherein a small amount of chlorine gas is added to the concentrated aqueous solution of the hydrazo compound, after the addition of water as required, acetone is added to form an acetone-water solution containing the hydrazo compound, and then chlorine gas is added to oxidize the hydrazo compound.
 11. A process according to claim 1, wherein the hydrazo compound contained in the concentrated aqueous solution has the following formula, ##STR2## wherein R stands for alkyl of 1 to 6 carbon atoms, M stands for Na or H, and n is an integer of 1 to
 6. 12. A process according to claim 1 wherein acetone or acetone and water cooled below 10° C. is or are added to the concentrated aqueous solution of a hydrazo compound.
 13. A process according to claim 1, wherein chlorine gas is added as the oxidant in an amount of at least 0.5 mole per mole of the keto-acid or its sodium salt.
 14. A process according to claim 13, wherein the oxidaion is carried out at lower than 30° C.
 15. A process according to claim 13 wherein chlorine gas is added at a temperature lower than 5° C.
 16. A process according to claim 1, wherein acetone is evaporated from the acetone-water solution containing the diazocyano acid and the diazocyano acid is separated and recovered from the residue.
 17. A process according to claim 16, wherein after evaporation of acetone, water is added to the residue in an amout of 100 to 1000 parts by weight per 100 parts by weight of the diazocyano acid.
 18. A process according to claim 16, wherein the diazocyano acid is separated and recovered at a temperature lower then 30° C.
 19. A process according to claim 1, wherein the diazocyano acid is isolated and purified.
 20. A process according to claim 19, wherein the purification is carried out by dissolving the isolated diazocyano acid in a mixed acetone-water solution at a volume ratio of from 75/25 to 95/5, evaporating acetone from the solution and washing the residue with water.
 21. A process according to claim 20, wherein the volume-ratio of acetone to water is from 75/25 to 90/10. 